https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=290773
Bug ID: 290773
Summary: vtnet: Severe performance regression since D51686
Product: Base System
Version: 14.3-STABLE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: [email protected]
Reporter: [email protected]
Hello,
I am experiencing a severe network performance regression on KVM-based
environments (like GCE and Proxmox) using vtnet (VirtIO) network interfaces.
Symptoms:
Network throughput (e.g., during an scp transfer) collapses to extremely low
speeds (approx. 3-4 KB/s).
The guest VM is not overloaded (CPU remains idle).
Root Cause (Specific Commit): This regression was introduced by commit:
a98b5f3ff34e7ff851f6127a64ebd88818c8d004
If I revert this single commit, network performance returns to normal, even
with TSO enabled.
Workaround (Confirms TSO issue): The issue is directly related to TCP
Segmentation Offload (TSO). Disabling TSO manually on the interface also
resolves the performance problem: ifconfig vtnet0 -tso
Steps to Reproduce:
Run a 14-STABLE kernel containing commit a98b5f3ff34e.
Host the VM on a KVM hypervisor.
Attempt to transfer a file from the VM using scp from another host.
Observe throughput drop to near-zero.
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